By: Elisabeth Ginsburg
All winter long, tomato lovers suffer, eating supermarket fruit with the taste and texture of foam packing peanuts. Finally summer arrives, bringing a harvest of tart, sweet, sunshiny tomatoes. You can buy these edible jewels at the local farmers’ market, but there is something incredibly satisfying about growing your own. A just-picked tomato, still warm from the sun is nirvana in a red wrapper.
But the path to that nirvana can be strewn with obstacles. Tomato plants are subject to a host of pests and diseases. Bacteria, viruses and fungi attack stalks, leaves and fruit, while insects make every attempt to rob gardeners of hard-won harvests. Even the best-regulated vegetable garden is not immune to tomato maladies.
Knowing the enemy, whether it is a pest, disease or disorder, is the first line of defense. Following good cultural practices is the second, and learning effective treatments for specific problems is the third.
So who are these enemies of the tomato?
Tomato Fungal Diseases
Fungi thrive in humid weather and poor air circulation. Several different types afflict tomatoes, most often manifesting themselves in the form of brown or black leaf spots.
Early blight generally starts on older foliage and shows up as small brown spots. Left untreated it can defoliate plants and rot fruit. Leaves also drop in the case of septoria leaf drop and leaf mold, both of which cause brown leaf spots. Buckeye rot and anthracnose show up on fruit, with brown spots in the case of buckeye rot and spots with salmon-colored spores in the case of anthracnose. Fusarium wilt kills the entire plant, with leaves losing color as the infection progresses. Southern blight also kills the entire plant and is distinguished by brown lesions on the lowest part of the stem.
Possibly the worst tomato disease is late blight, which not only kills entire plants, but is highly contagious, with spores that spread by wind. Caused by the Phytophthora infestans fungus, the disease manifests itself in the form of bullseye-type spots on leaves. If you suspect late blight, get a positive identification from the nearest cooperative extension agent. Once the identification is made, all infected plants should be destroyed (not composted). If neighbors raise tomatoes or potatoes, it is helpful to notify them as well. Keep vigilant for signs of the disease on unaffected plants.
Tomato Bacterial and Viral Diseases
Tomatoes can also be stopped in their tracks by bacterial and viral diseases. One of them is bacterial wilt, which causes a generalized decline of affected plants. Another is bacterial spot, which produces brown leaf spots and scabby patches on fruits.
Spread by thrips, tomato spotted wilt virus shows up in the forms of spotted leaves and discolored fruits that fail to ripen properly. Whiteflies harbor tomato yellow leaf curl virus, which results in curled, misshapen leaves, sudden blossom drop and stunted fruit. Tobacco mosaic virus causes mottled, misshapen leaves and plant weakness.
Insect predators of tomato include aphids, which attach themselves to stems and leaves and suck out the plant’s juices. Tomato fruitworm larva develop inside fruits, making them inedible, and large, ugly tomato hornworms dine voraciously on stems and leaves, before taking on fruits.
Colorado potato beetles are another pest that will go for tomatoes when potatoes are not available. The striped yellow and brown beetles lay clusters of golden-orange eggs below leaves and orange and black larvae quickly emerge–both will eat tomato leaves and fruit.
Other Tomato Problems
Tomatoes can also be afflicted by blossom end rot, which causes rot that begins at the bases of fruits. It is caused by calcium deficiency, so feeding your tomatoes well will stop this common physiological problem.
Tomatoes with growth cracks and catfaced tomatoes with abnormal bulges and cavities are not diseased. Instead it’s environmental factors that mar the appearance and viability of the fruit. Water cracking is also a problem that occurs on fully developed fruits after heavy rain. Excess water fills the fruits and causes them to crack on the vine. And if defoliation occurs on plants, tomatoes are susceptible to being marred by sun scald, which causes fruits to develop light watery spots in high sun exposure.
So…What Can You Do?
The first line of defense against pests and diseases is extremely cheap and relatively easy—good cultural practices. Start with the tomato seeds or visibly strong, healthy plants and choose disease resistant varieties. Remember that not all varieties are resistant to all diseases. Local cooperative extension or nursery personnel can help with questions about tomato diseases prevalent in your area and which varieties are most resistant to those diseases.
Once you choose your tomatoes, plant them in good soil, enriched with a high-quality amendment like Fafard® Garden Manure Blend. Space plants so that they have plenty of air circulation (15-24 inches apart) and use tomato cages or other supports to get plants and fruits up off the ground. Water regularly, especially during dry periods, and prevent the spread of spore-borne diseases by using soaker hoses to water at ground level.
Be alert for signs of fungal diseases and if they appear, remove and destroy affected plant parts. Do not compost them. At the end of the growing season, remove all plant parts and debris, so that spores do not overwinter in the soil. From year to year, practice crop rotation to discourage pathogens. If you are growing tomatoes in containers, start each season with fresh soil, after washing containers with a solution of one part household bleach to nine parts water.
Anti-fungal solutions, including organic mixtures, are available at nurseries and garden centers. Depending on the compound, the anti-fungal remedy can be used as a preventive measure or to stop the spread of fungus on affected plants. Either way, follow manufacturers’ directions carefully.
Some people swear by homemade fungal deterrent sprays, including one made with one tablespoon of cider vinegar per gallon of water. Apply every few days to stems as well as tops and bottoms of leaves. Another popular kitchen-based fungal remedy calls for one tablespoon of baking soda per gallon of water, augmented with two tablespoons of vegetable oil and a few drops of dishwashing liquid. Shake the mixture will and apply with a spray bottle every few days and after rainstorms.
Dispatch aphids with a strong spray from a hose, or spray plants with insecticidal soap, following package directions. Watch for tomato fruitworms and hornworms on plants. Check for holes in leaves or fruit and destroy any that show signs of damage. Hand pick the worms and drop them into containers of soapy water. Wear gloves for this job. If you are squeamish about handling these wriggly creatures, remember that when it comes to beating pests and diseases, the end justifies the means. The taste of a sweet summer tomato will make you forget all about worms and wilts.
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